Chemical mechanical polishing, or CMP, is a method often utilized to polish wafers of ceramics, silicon, glass, quartz, and metals. CMP pads have a working surface, used to contact the object to be polished, that has a large number of small asperities. CMP generally involves applying the object to be polished, e.g. a wafer, against a rotating porous pad having asperities that is made from a durable organic substance. A chemical slurry is utilized that contains a chemical capable of breaking down the wafer substance and an amount of abrasive particles which act to physically erode the wafer surface. The mechanical aspect of polishing occurs from abrasive particles, typically included in the chemical slurry, and the chemical aspect of polishing is generally oxidation that occurs of metal to ease in mechanical removal. The slurry is continually added to the rotating CMP pad, and the dual chemical and mechanical forces exerted on the wafer cause it to be polished in a desired manner.
Many CMP pads are made of porous urethane. Often, such CMP pads include about ⅓ by volume pores. During processing, the pores interact with the chemical slurry and abrasive particles to retain them on the working surface of the CMP pad. Ideally, the porous structure of a CMP pad works to effectively retain at least a portion of the chemical slurry. Unfortunately, many designs cause slurry leak through the pad due to the construction of the pores of the CMP pad.
As semiconductor technology continues toward size reduction to the nano-scale, however, current CMP polishing techniques are proving to be inadequate. With such a reduction in scale, materials utilized to construct circuit elements have become more delicate, both in size and materials. The CMP industry has been required to respond by providing polishing materials and techniques that accommodate these advances. For example, lower CMP polishing pressures, smaller size abrasive particles in the slurry, and polishing pads of a size and nature that do not over polish or damage the wafer must be used. Furthermore, proper distribution of slurry is needed to prevent heat damage to the material of the CMP pad, to provide proper chemical polishing, and to provide proper mechanical polishing due to the abrasive particles.